I’m having trouble grasping why small polar molecules can cross the hydrophobic region of the membrane and not ions. Won’t the polar molecules be attracted to the watery extracellular medium and not be inclined to move through the hydrophobic region? (This is my reasoning for why ions won’t go through.)
Also, why do lipid-soluble particles go through the membrane? I understand they have an affinity for the hydrophobic region, but won’t they want to stay there, sandwiched between the two watery layers? Isn’t that the point of the orientation of the bilayer? Why would the lipid-soluble particles move from the hydrophobic region into the watery interior of the cell? Furthermore, why are lipid molecules not repelled by the hydrophilic heads on the exterior of the membrane?
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